Robrow

I must say interesting actuators, are they screw jacks?

The type of linear servo I am talking about had the option of rotary or linear output and the same format as our current rotary only output servos. Speed/power were the same, they were more popular when I first started saving my paper round money to buy some 30-40 years ago.

Rob.

olnico

Yes Rob, they are screw jacks.

The problem with the servos that you describe above is that they translate the motor rotational movement to a translation movement via a toothed rack.
As far as I am aware of, toothed racks in high speed/ high power applications ( like steering racks ), need ball tracks to be able to operate at the given speed and power requirements. However, given the size of the racks in our servos, this would have been a real problem. This is why this design stayed to low power servos and was later dropped.

Robrow

Yes, that was probably the reason, maybe now we have the components/technology to make them viable again for our requirements.

Rob.

HarryC

My Feedback: (1)

Olnico, those are not screw jacks, they are rack and pinion. A screw jack is a threaded rod with what is effectively a nut running back and forward along it. Screw jacks can be plenty fast enough for primary control, the tailplanes on the Tornado are driven by screw jacks.

Jetpilot24

My Feedback: (21)

Colin Those are it. I have used them before and they work very good with no slop.

Thanks
Joe L.

olnico

Harry, please read the thread.

Rob was referring to my previous post:
http://www.rcuniverse.com/forum/fb.asp?m=9379511

Where I was explaining the limitations of this:
http://www.firgelli.com/products.php


If you know any electrical type linear servo that can achieve a linear speed of 30 mm/s and generate a force of 45N or more within the volume and the weight of a model servo ( around 20 grams and 45 mm x 15 mm x 20 mm ), I'd be extremely interested to get its reference.

Robrow

A hydraulic system would be an interesting proposition, there are hydraulic landing gear hydraulic systems available.

Rob.

marc s

Rob,

I installed a Hausll system in a large MB339 for Ali a couple of years ago, although reasonably good it was a pain to install, and required oil and pressurised air to work so you had two 'components' to control and deal with. Fortunately the landing gear was all mounted in the main fuselage section so no breaks were required in the pipe connections, where a jet has gear mounted in the removable wings another problem and potential leak area presents itself.

It gear motion was very scale looking I have to say.

marcs

David Gladwin

Rob,

Dont even THINK of going there and I speak after years of using 3 types of hyd systems on my FC Mig 29 !

regards, David.

invertmast

My Feedback: (23)

I'd like to hear some more indepth review of these 3 systems you've used. As I am planning on using the hausl system in my F-14 for its landing gear, doors and speedbrakes.

Robrow

He..he..ok I guess maybe not []

Looks like the basis of a hydraulic system is there, the accumulator looks like it is air pressurised.

Rob.

David Gladwin

System 1. the FC system as for the Mig 29, I couldn't get it to work at all reliably, I was most certainly not alone (I saw Wolfgang Kluhr having problems too !) although Andreas Geitz said it was all my fault. One of the many others was the Omega team from South africa, Francois Deidreschen and others who redesigned it and it works very well creating :
System 2 Works very well, but the pump gave rather slow retraction speeds on the gears but was otherwise fine for flight. Pump running time was timer based. The next system and my current one is
System 3 The Omega but with Hausl pump. This is a constant pressure system which uses a small accumulator with pressure switch, and large accumulator, so that the pump "on" is commanded by pressure rather than timing . The Omega controller controls the locking valves and CAN be replaced by a Jettronics sequencer. This is my current fit on my Mig 29, and produces acceptable travel times on the gear.

Based on this experience I cannot see us using hydraulic systems on flight controls in the foreseable future as with the new brushless and high power digital servos I see absolutely no advantage and LOTS of problems as we do not, for example, have engine driven pumps as do fullsize aircraft

Has anyone yet used the new JR digital (6301) servos and brushless units, or HV servos ?

Regards,

David.